3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF ETHYLENIC TETRATHIAFULVALENE DERIVATIVES

The degenerate four-wave-mixing method is used to measure the second-o rder hyperpolarizabilities gamma of new soluble tetrathiafulvalene (TT F) derivatives. For each material, the study of solutions at various c oncentrations leads to the choice of an optimum solution: a compromise between 'low-nonlinearity low-loss' and 'high-nonlinearity high-loss' solutions and thus to the determination of its susceptibility chi([3] ). The hyperpolarizabilities are deduced from these measurements; ethy lenic TTF derivatives show gamma(electronic) values as large as - 7.58 X 10(-45) (MKS), larger than acetylenic TTF derivatives which have ga mma(electronic) = -1.12 X 10(-45).